This invention relates generally to plastic bottles for the retention of fluids under pressure such as carbonated beverages or the like. The invention particularly relates to an improved integral base for such bottles.
During the last twenty years or so, there has been a dramatic shift in the packaging of carbonated beverages, particularly, soft drinks, away from glass containers and toward plastic containers. The plastic containers initially took the form of a two-piece construction wherein a plastic bottle included a generally hemispherical bottom to which was applied a separate base cup which would permit the bottle to stand upright. The hemispherical bottom was seen as the most desirable shape for retaining the pressure generated by the carbonation within the beverage. The pressures can rise up to 100 p.s.i. or more when the bottled beverage is exposed to the sun, stored in a warm room, car trunk, or the like. Such plastic containers represented a significant safety advantage over glass containers when exposed to the same internal pressures. However, the two-piece construction was not viewed as optimum inasmuch as it required a post molding assembly step, and, generally, a separation step prior to reclaiming or recycling of the resins forming the bottle and base cup.
During this period of development, various attempts were made to construct a one-piece, self-supporting container which would be able to retain the carbonated beverages at the pressures involved Such a one-piece container requires the design of a base structure which would support the bottle in an upright position and would not bulge outwardly at the bottom. A variety of designs have been attempted following one of two principal lines of thought. One line of designs involved a so-called champaign base having a complete annular peripheral ring. Examples of such bottles are found in U.S. Pat. Nos. 3,722,726; 3,881,621; 4,108,324; 4,247,012; and, 4,249,666. Another variety of designs is that which includes a plurality of feet protruding downward from a curved bottom. Examples of this variety are to be found in U.S. Pat. Nos. 3,598,270; 4,294,366; 4,368,825; 4,865,206; and, 4,867,323.
Bottles using each of these general designs have, in the past, shown significant drawbacks. In order to prevent involution of the bottom of bottles using a champaign style, it was generally found necessary to incorporate a significant amount of resin in the base of the bottle thereby ensuring its stability at room temperature. This incorporation of significant amounts of resin in the base of the bottle had the effect of not only increasing the cost of the bottle, but also making it increasingly subject to drop impact failure.
Reasonably stable footed bottles could be made employing less resin, but the uneven orientation of the polymer in the footed area of the bottom often contributed to uneven post filling expansion of either one or more feet or the central portion of the bottom creating what is generally referred to as a "rocker." Further, it was recognized that the stability of the bottle was directly related to the size of the footprint of the bottle. Whereas some of the earlier designs were in the form of a plurality of nearly point-like feet spaced apart by about half the diameter of the bottle, more recent designs have tended toward a wider spacing of the feet with each foot designed to contact an increased area of the underlying surface.
Throughout the development of various improvements on the two basic designs has been the constant goal to develop a container of stable configuration using as little resin as possible thereby reducing the cost of the container while maximizing the utility of natural resources.